From: Jonathan Paisley <jp-www@...>
Date: 2004-12-08T02:42:31+09:00
Subject: Re: Idiom for creating hash from two arrays

On Tue, 07 Dec 2004 15:08:50 +0100, Robert Klemme wrote:

> "Jonathan Paisley" <jp-www@dcs.gla.ac.uk> 

>>   h = Hash[*keys.zip(values).flatten]
>>   #=> {"three"=>3, "two"=>2, "one"=>1}
>>
>> Can anyone suggest a better way of doing this? I'm slightly put off by
>> the many steps involved in my present solution.
> 
> Here are some others - but IMHO your solution is much nicer:
>>> h={}
> => {}
>>> keys.each_with_index {|e,i| h[e]=values[i]}
> => ["one", "two", "three"]
>>> h={}
> => {}
>>> keys.inject(values) do |v,k|
> ?>   h[k]=v.shift
>>>   v
>>> end

Of these (including my original), I think the each_with_index solution 
is the most transparent and readable, but I don't like having to
separately initialize h beforehand. I think I'll stick with what I've 
got for now, or perhaps implement:

def Hash.from_pairs(keys,values) # or some better name
  h = {}
  keys.zip(values) do |k,v|
    h[k] = v
  end
  h
end

(using zip with a block has just occured to me)

I did some benchmark tests of all four implementations (my original, 
your two, and the above). The last is about twice as fast as 
each_with_index and inject, and at least an order of magnitude faster 
than my original method involving flattening.

Many thanks for your input! Most appreciated.